﻿//
// Copyright (c) 2011 Canyala Innovation AB
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this software and 
// associated documentation files (the "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 
// copies of the Software, and to permit persons to whom the Software is furnished to do so, 
// subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT 
// NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH 
// THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. 
//

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;

namespace Canyala.Lagoon.Expressions
{
    public class Interpreter
    {
        public static double Evaluate(string expression, Symbols symbols = null)
        {
            if (symbols == null)
                symbols = new Symbols();

            Interpreter interpreter = new Interpreter(expression, symbols);
            return interpreter.Value;
        }

        public Interpreter(string expression, Symbols symbols = null)
        {
            if (symbols == null)
                symbols = new Symbols();

            Tokens = new Tokenizer(expression);
            Symbols = symbols;
        }

        public double Value 
        { 
            get 
            {
                Tokens.Initialize();
                return InterpretExpression(); 
            } 
        }

        public Symbols Symbols { get; set; }
        private Tokenizer Tokens;

        private double InterpretExpression()
        {
            double value;

            if (Tokens.Accept(token => token == "+"))
                value = InterpretTerm();
            else if (Tokens.Accept(token => token == "-"))
                value = -InterpretTerm();
            else
                value = InterpretTerm();

            while (Tokens.Allow(token => token == "+" || token == "-"))
            {
                switch (Tokens.Read())
                {
                    case "+":
                        value = value + InterpretTerm();
                        break;
                    case "-":
                        value = value - InterpretTerm();
                        break;
                }
            }

            return value;
        }

        private double InterpretTerm()
        {
            double value = InterpretFactor();

            while (Tokens.Allow(token => token == "*" || token == "/"))
            {
                switch (Tokens.Read())
                {
                    case "*":
                        value = value * InterpretFactor();
                        break;
                    case "/":
                        value = value / InterpretFactor();
                        break;
                }
            }

            return value;
        }

        private double InterpretFactor()
        {
            double value;

            if (Tokens.Accept(token => token == "("))
            {
                value = InterpretExpression();
                Tokens.Expect(token => token == ")");
            }
            else
            {
                if (Tokens.Allow(token => char.IsDigit(token[0])))
                {
                    value = Double.Parse(Tokens.Read(), CultureInfo.InvariantCulture.NumberFormat);
                }
                else if (Tokens.Allow(token => char.IsLetter(token[0]) || token[0] == '°'))
                {
                    value = Symbols.ValueOf(Tokens.Read());
                }
                else
                {
                    value = InterpretExpression();
                }
            }

            return value;
        }
    }
}
